There are numerous requirements for orienting space craft but space by its very nature offers no base from which to apply force. It has been the conventional practice to use small jets to accelerate materials and produce reaction forces to cause the space craft to be oriented. However, the ejection of such materials can produce debris in the vicinity of the space craft such that the debris interferes with the collection of reliable scientific information. The need to carry fuel for the jets adds to the weight penalty for the space craft which in turn increases the launch vehicle weight and cost.
Reaction engines of several types have been developed ranging from very small jets using evaporation of liquids or deliquescence of solids to larger liquid fuel chemical reaction yet. Various types of devices requiring acceleration of flywheels have also been developed, but these suffer from weight and ultimate strength of material limitations, as well as high speed bearing requirements. The cost and mechanical limitations of such devices have limited their usefulness. Radiation pressure applied to off-center panels has been considered, but this has proven to be too slow for most applications.
Therefore, there exists a need for an orientation device which can reliably and accurately orient a space craft without the need to eject materials while having a small number of high reliability components. Such a device should preferably be electrically powered rather than powered by means of stored chemical fuel.